Radiation Exposure
In Nuclear Medicine
Darlene Metter, MD FACR
DISCLOSURE STATEMENT
I have no relevant financial
relationships with commercial
interests to disclose.
Ionizing Radiation in Medical
Imaging
•
•
•
•
> 100 years
Beneficial to patient care
New & emerging technologies
Revolutionized the practice of
medicine
Learning Objectives
• Describe the trends in the use of NM
procedures
• Identify major sources of radiation
exposure to:
• the patient
• the technologist
• List 3 occupational radiation safety dose
strategies for the NM technologist
Pre-Test
Question #1
• In 2006, the average annual radiation
exposure in the US from medical
imaging is estimated at:
•
•
•
•
A. 30%
B. 40%
C. 50%
D. 60%
Question # 2
• Which one of the following is an
example of a non-stochastic radiation
effect?
•
•
•
•
A. Cataracts
B. Cancer
C. Genetic defects
D. Autism
Question # 3
• Which one of the following exams has
the highest pt radiation exposure?
•
•
•
•
A. Cardiac (201Tl 4 mCi)
B. Cardiac (99mTc 40 mCi, 1 day)
C. Octreoscan (111In 6 mCi)
D. F18 FDG 20 mCi
Question # 4
• Which NM technologist task is
generally associated with the highest
work-related dose?
•
•
•
•
A. Radiopharmaceutical preparation
B. Radiopharmaceutical injection
C. Patient scanning
D. Patient transfers
Question # 5
• Which NM procedure is generally
associated with the highest
occupational dose to the NM tech?
•
•
•
•
A. Bone SPECT
B. MUGA
C. 131I WB post therapy scan
D. Stress 99mTc MIBI
Current Trends/Usage of
NM Procedures
Current Trends/Usage of NM
Procedures
• 2007 US medical procedures:
highest source of ionizing radiation
to the public
• Inc in diagnostic imaging using
ionizing radiation (F Mettler, 2008)
– CT, vascular interventional, NM
ACR Response: White Paper*
• 2007 ACR Blue Ribbon Panel on
Radiation Dose in Medicine
• To assess current dose issue in
medical procedures
• Develop guidelines to protect &
inform the public
Amis et al “ACR White Paper on Radiation Dose in Medicine”
2007 JACR Vol 4 (5). P 272-284
ACR Panel Conclusion
1. Education of stakeholders in
radiation safety
2. Appropriate utilization of imaging
3. Standardization of radiation dose
data for archiving: benchmarking
good practice
4. Identify pts who have reached
certain thresholds; alternate imaging?
Includes Nat Acad of Science; Nat Acad of Engineering; IOM;
National Research Council
1.5 day meeting with ACR input
Increasing public concern*
* SNM Smart Brief 11/28/2011
ACR Panel Report
• 1980
• 2005
• CT 3 million
• NM 7 million
• CT 60 million
• NM 20 million
Est # NM Exams (X1000) (US)*
1970
Brain
1250
GU
110
Bone
80
Lung
330
Thyroid
450
CV
25
Total
3230
Pop (106)
209
1975
2100
150
220
600
630
50
4800
215
1980
870
200
1300
900
650
600
5850
227
2005
<100
470
3450
740
<100
9800
19,000
300
• Mettler FA 2008 “Medical Effects of Ionizing Radiation
Est # NM Exams (X1000) (US)*
1970
Brain
1250
GU
110
Bone
80
Lung
330
Thyroid
450
CV
25
Total
3230
Pop (106)
209
1975
2100
150
220
600
630
50
4800
215
1980
870
200
1300
900
650
600
5850
227
2005
<100
470
3450
740
<100
9800
19,000
300
• Mettler FA 2008 “Medical Effects of Ionizing Radiation
Est # NM Exams (X1000) (US)*
1970
Brain
1250
GU
110
Bone
80
Lung
330
Thyroid
450
CV
25
Total
3230
Pop (106)
209
1975
2100
150
220
600
630
50
4800
215
1980
870
200
1300
900
650
600
5850
227
2005
<100
470
3450
740
<100
9800
19,000
300
• Mettler FA 2008 “Medical Effects of Ionizing Radiation
Gamma Camera Sales
• 11/23/11 Global Industry Analysts, Inc
• Report: global market for gamma cameras
projected to inc to $846.6 million by 2017
• US is the largest global market
• Why? Aging pop, inc death rate assoc w/
cancer, cardiac & CNS disease
• Inc public awareness of advanced imaging
What About PET?
• Bio-Tech Sys of Las Vegas:
market researcher providing
insight into new technologies &
trends
• Predict: PET procedures to
increase
• SPECT: 2010 $758 million to 2018 $1.68 billion
Why?
• Wider availability of FDG & PET
technology
• Wider physician & patient acceptance
• Increased approved indications (ie
reimbursement)
• Emerging novel tracers: oncology,
cardiology, neurology
PET Procedures
• 2009: increase 9%
• 2010: increase 9%
• PET agents:*
– 2010 $391.8 million
– 2018 $4.31 billion
• CMS reimbursement issues, but PET
users adapted to reimbursement
requirements**
* Bio-Tech Systems
** NOPR 2006-09 expanded CMS coverage; NOPR 2009
FDG Sales
• Reflection of PET procedures
• 2009: $300 million for FDG
• 2017: projected $800 million for
FDG
• 2017: projected $3.43 billion for
all PET RP
Average Annual Radiation
Exposure*
• 1987: radon/NORM majority
medical imaging 15% (XR, NM)
• 2006: medical imaging 51%
radon 30%
internal/therapies 6%
cosmic 6%
* Mettler FA 2008 “Medical Effects of Ionizing Radiation”
Average Annual Radiation
Exposure*
• 1987: radon/NORM majority
medical imaging 15% (XR, NM)
• 2006: medical imaging 51%
radon 30%
internal/therapies 6%
cosmic 6%
• US avg: 6.27 mSv/y (WW: 2.4 mSv/y)
• Mettler FA 2008 “Medical Effects of Ionizing Radiation
Radon
• Decay product of uranium
• t½: 4.5 billion yr
• Largest component in background radiation,
granite bedrock (earth’s crust)
– 3 mSv or 300 mrem/yr per person in US
• Gas accumulating in buildings:
– attics, basements
– indoor air contaminant
– Texas: low–mod potential
NO high potential
San Antonio
Orlando
ACR Panel Report
• Japanese atomic bomb survivor data
– most compreh epidem study supporting
radiation induced carcinogenesis
• Statistically signif inc in CA at doses >
50 mSv; below ?? - controversial
• CT-NM studies dose estimates: 10-25
mSv/study
• Implication of multiple studies
ACR Panel Report
• “1 yr collective dose estimate from
medical procedures in the US = total
WW collective dose generated by the
nuclear catastrophe at Chernobyl”
ACR Panel Report
• Radiation induced CA latency: 10-20
years or longer
• Effects of current inc dose not evident
for many years
• Difficult to attribute “radiation induced
CA” from a study from normal risk*
~ 40% of population dx w/ CA in lifetime
* Can’t distinguish radiation induced CA from others
Review: Trends in NM Procedures
• Since 1980, inc number of NM proced
• Major sources of radiation to public:
–A
medical
exposure,
background
SIX fold increase in 26 years!
radiation & radon
• Mettler (2008) population per caput
Or a 600% increase in one
annual dose from medical radiation:*
generation
– 1980: 0.54 mSv
– 2006: 3.2 mSv (> bkgd 2.3 mSv)
* Huda W, Mettler FA Radiol: Vol 258(1) Jan 2011; p 236-242
Question #1
• In 2006, the average annual radiation
exposure in the US from medical
imaging is estimated at:
•
•
•
•
A. 30%
B. 40%
C. 50%
D. 60%
Question #1
• In 2006, the average annual radiation
exposure in the US from medical
imaging is estimated at:
•
•
•
•
A. 30%
B. 40%
C. 50%
D. 60%
NM PROCEDURE DOSES
TO: the PATIENT
Courtesy L Gordon, MD Med Univ of SC
Understanding Patient Exposure
• Most physicians do not understand
• Goal: education; can then weigh a
procedure’s risks & benefits
• Mettler:
– NM study avg pt dose: 0.3-20 mSv
– average annual effective dose from
background radiation: 2.5-3 mSv
Radiation Protection in US
• Before 1950, concern was
occupational exposure
• Mid-1950s, public concern included
- patient & individual
- population: progeny, genetic pool
as a whole
Terminology
1. Stochastic vs Non-stochastic
effects
2. Quantification of radiation
exposure
Stochastic Effects*
• “Effects that occur by chance,
generally occurring without a
threshold level of dose, whose
probability is proportional to the dose
and whose severity is independent of
the dose. In the context of radiation
protection, the main stochastic effects
are cancer and genetic effects.”
NRC website: www.nrc.gov
Stochastic Effects
• Uncertain if chronic low dose
radiation leads to adverse latent
effects: CA
• Appears most low dose radiation →
cellular repair → no adverse effects
• What are the adverse cellular effects
of radiation?
Radiation: Adverse Cellular Effects
• Cells vary in radiosensitivity (“cell death”*)
– degree of proliferation, differentiation,
duration of mitosis
• Cell radiosensitivity: function of cell type
– Low: non-dividing, fixed post-mitotic
• mature RBC, bone, cartilage
• muscle, ganglion cells
• mature connective tissue
• Radiation cell death caused by the double-stranded
DNA break
Radiation: Adverse Cellular Effects
• High: less differentiated, divide quickly
• Lymphocytes, immature
hematopoietic, intestinal
epithelium, spermatogonia, ovarian
follicular cell
BEIR Committee
• National Academy of Science:
Biological Effects of Ionizing
Radiation Committee
• Claims future CA risk for low level
ionizing radiation uses a nonthreshold, linear model for cancer
induction
• Data: atomic bomb survivors
BEIR VII*
• Supports “linear-no-threshold” model
• CA risks proceeds linearly at low
doses w/o a threshold, smallest dose
has the potential to cause a small inc
in CA risk
• Low dose: up tp 100 mSv
* Biologic Effects of Ionizing Radiation (June 2005), Nat Acad Sciences
100 people
BUT other 42 are
naturally occurring.
One
100 mSv
exposure
1 Cancer
Background Cancer in Population
• Cancer diagnosis: ~ 42/100 people
• 1/1000 could be from a single 10 rem
(0.1 Sv) dose above background
radiation*
• Since the BEIR Committee assumes
the linear no threshold model, risks
from cancer can be calculated
* BEIR VII report
Stochastic Effects
• But there appears to be a threshold to
adverse effects at 0.05-0.1 Sv, but to
be conservative, NRC assumes:
– no threshold
– linear response
– ALARA principle
ALARA Principle
• “As-Low-As-Reasonably-Achievable”
• 3 tenets: time, distance, appropriate
shielding
• ALARA I: 125 mrem/quarter
• ALARA II: 375 mrem/quarter
• Helps to set “checkpoints,” if reached
should justify investigation & action
Non-Stochastic Effects*
• “ The health effects of radiation, the
severity of which vary with the dose
and for which a threshold is believed
to exist. Radiation-induced cataract
formation is an example of a nonstochastic effects (also called a
deterministic effect).”
NRC website: www.nrc.gov
Radiation Cataractogenesis
•
•
•
•
•
Non-linear
Dose-related threshold:~2 Gy/200 rad
Doses > 7 Gy: 100% cataracts
Latency: ~ 15 yrs
High LET, greater RBE (factor 2 or >)
– e.g. shorter duration at a higher
dose, faster cataract formation
Radiation Effects
• Stochastic
• Non-stochastic
• Severity:
independent of
dose
• Probability of
occurrence: inc
with dose
• Threshold: No
• Severity: increases
with dose
• Probability of
occurrence: inc
with dose
• Threshold: Yes
Question # 2
• Which one of the following is an
example of a non-stochastic radiation
effect?
•
•
•
•
A. Cataracts
B. Cancer
C. Genetic defects
D. Autism
Question # 2
• Which one of the following is an
example of a non-stochastic radiation
effect?
•
•
•
•
A. Cataracts
B. Cancer
C. Genetic defects
D. Autism
Quantification of
Radiation Exposure
Quantification of Radiation
Exposure
•
•
•
•
•
Measured quantities
Exposure
Absorbed dose
Equivalent dose
Effective dose
Quantification of Radiation
Exposure
• Measured quantities: (Curie, Ci;
Bequerel, Bq) administered activities
• Exposure
• Absorbed dose
• Equivalent dose
• Effective dose
Quantification of Radiation
Exposure
• Measured quantities
• Exposure: (Coulomb/kg; Roentgen,
R) exposure in air; amt of X- or
gamma rays producing a given amt of
ionization in each unit of air
• Absorbed dose
• Equivalent dose
• Effective dose
Quantification of Radiation
Exposure
• Measured quantities
• Exposure
• Absorbed dose: (Gray, Gy; rad) amt
of energy absorbed per unit mass
• Equivalent dose
• Effective dose
Quantification of Radiation
Exposure
•
•
•
•
Measured quantities
Exposure
Absorbed dose
Equivalent dose: (Sievert, Sv, rem)
absorbed dose X quality factor; QF for
photons = 1 (beta, gamma); quantifies
biologic harm to tissue related to type of
radiation
• Effective dose
Quantification of Radiation
Exposure
•
•
•
•
•
Measured quantities
Exposure
Absorbed dose
Equivalent dose
Effective dose: (Sievert, Sv; rem) equiv
dose X tissue weighting factor; whole body
dose estimates via dose to & sensitivity of
each organ; calculated; allows comparison
between ionizing radiation sources
Effective Dose
• “Individual dose is best calculated by
determining the mean doses to all
radiosensitive tissue combining with age,
sex & organ specific coefficients.”
• Example:
– avg EDE background radiation: 2.5
mSv/y
– EDE chest xray: ~ 0.1 mSv
– Annual dose near Chernobyl: ~ 6 mSv/y
Effective Dose
• Calculations based on
anthropomorphic phantoms with
internal dosimeters or by the Monte
Carlo method of computational
algorithms – easy to measure
• Patient actual dose from a NM
procedure: very difficult
American Nuclear Society
NM Procedures : Sources of
Patient Doses
1. General NM
2. CT:
– SPECT/CT
– PET/CT
3. PET tracers
5 min
NM Procedures : Sources of
Patient Doses
1. General NM
2. CT:
– SPECT/CT
– PET/CT
3. PET tracers
Est # NM Exams (X1000) (US)*
1970
Brain
1250
GU
110
Bone
80
Lung
330
Thyroid
450
CV
25
Total
3230
Pop (107)
209
1975
2100
150
220
600
630
50
4800
215
1980
870
200
1300
900
650
600
5850
227
2005
<100
470
3450
740
<100
9800
19,000
300
• Mettler FA 2008 “Medical Effects of Ionizing Radiation
Growth in Imaging
• CARDIAC
• BONE
• 1970: 25,000
• 1970: 80,000
• 2005: 9,800,000 • 2005: 3,450,000
• Effective dose: ~ • Effective dose:
10 mSv or 1 rem
5.2 mSv (24 mCi
MDP)
Effective Dose in NM Imaging
•
•
•
•
> 85% labeled with Tc99m
100-1100 MBq (2.7-29.8 mCi)
ED: 1-10 mSv
PET/CT ED: 20-37 mSv (2-3.7
rem)
– FDG: 14.1 mSv (20 mCi)
– CT: 10-15 mSv
Effective Doses in NM
•
•
•
•
•
•
Brain: HMPAO
FDG
Thyroid: 123I
TCO4
Parathyroid
MUGA
ED (mSv)
6.9
14.1
1.9
4.8
6.7
7.8
mCi
20
20
0.15
10
20
30
Effective Doses in NM
• Cardiac: 201Tl
•
MIBI (2 d
•
MIBI (1d)
•
•
FDG
• Lung: MAA
133 Xe
•
•
DTPA
• GI Bleed
ED (mSv)
37
12.8
9.4
11.4
14.1
2
0.5
0.2
7.8
mCi
4
40
30
40
20
5
20
35
30
Effective Doses in NM
• Renal: DTPA
•
MAG3
•
DMSA
•
GH
• Bone:
•
•
ED (mSv)
1.8
2.6
3.3
2.0
6.3
5.2
3.5
mCi
10
10
10
10
30
24
16
Effective Doses in NM
•
•
•
•
•
•
•
•
ED (mSv)
67Ga
15
Octreoscan
26
WBC: 111In
7
HMPAO
8.1
Tumor: FDG
14
PET/CT
37
MIBG: 131I
7.4 mSv/mCi
123I
0.67 mSv/mCi
mCi
4
6
0.5
20
20
0.5-1
5-10
Effective Doses in NM
•
•
•
•
•
•
•
•
ED (mSv)
67Ga
15
Octreoscan
26
WBC: 111In
7
HMPAO
8.1
Tumor: FDG
14
PET/CT
37
MIBG: 131I
7.4 mSv/mCi
123I
0.67 mSv/mCi
mCi
4
6
0.5
20
20
0.5-1
5-10
111In
•
•
•
•
•
Octreotide SPECT/CT*
Package insert, 70 kg pt
4.35 mSv/mCi
6 mCi = 26 mSv (SPECT)
CT: 10 mSv
SPECT/CT: 26 + 10 = 36 mSV
•Sheu et al U of Pittsburgh MC “SPECT/CT and PET/CT: What Radiation
Dose are Your Patients Getting and What Does It Mean to Them? 2010 RSNA
NM Imaging
• So what does this all mean?
• How does one quantitate this?
• How does this relate to one’s
cancer risk?
ACR Website
• Equates studies with a time equivalent of
background radiation and cancer risk
• NOTE: 1 in 5 will die from CA
• Risk of dying from CA due to exam:
- v low: 1 in 104 to 105
- low: 1 in 103 to 104
- moderate: 1 in 500 to 103
Equivalence (background radiation)
and CA Risk
•
•
•
•
•
•
•
•
•
•
Abd/pelv
Abd/pel: -/+
Coronary CTA
Ca++ score
CT colon
BE
Spine
Chest
Chest CTA/PE
Head
15 mSv 5 yr
30
10
16
5
3
1
10
3
8
3
6
2
7
2
15
5
2
8 mo
low
mod
low
low
low
low
low
low
low
v low
Extrapolate the Dose to NM
procedures
• Mod risk: 201Tl 37 mSv: 4 mCi
Octreoscan SPECT/CT:
36 mSv
FDG/PET CT: 20-37 mSv
67Ga 30 mSv: 8 mCi
• Risk of dying from CA: 1 in 500 to 1000
Extrapolate the Dose to NM
procedures
• Low risk: Cardiac 99mTc (MPI, MUGA)
•
MDP, WBC
•
Brain HMPAO/FDG
•
V/Q, GI & GU
•
MIBG, Thyroid/parathyroid
• Risk of dying from CA: 1 in 1000 to
10,000 (from the exam)
Procedure Equivalence (CXR)
•
•
•
•
•
•
•
Study
Eff Dose (mSv)
Dental
0.005-0.01
CXR
0.1
MMG
0.4
CT
2-16
NM
0.2-41
Interventional
Fluoroscopy
>70
# CXR
0.25-0.5
1
20
100-800
10-2050
250-3500
Question # 3
• Which one of the following exams has
the highest pt radiation exposure?
•
•
•
•
A. Cardiac (201Tl, 4 mCi)
B. Cardiac (99mTc , 40 mCi, 1 day)
C. Octreoscan (6 mCi)
D. F18 FDG 20 mCi
Question # 3
• Which one of the following exams has
the highest pt radiation exposure?
• A. Cardiac (201Tl, 4 mCi)
CT Dose Reduction
CT Acquisition Parameters
• kVp: kinetic energy of the electron;
inc kVp → inc dose; inc penetrating
power; dec contrast (~ 120 kVp)
• mAs: photon flux; inc mAs → inc #
photons, inc dose (~ 120 mAs or >)
• Pitch: how far CT table travels per
xray source rotation; inc pitch → dec
dose: dec z-axis resol + recon artifact
Which Parameter Has a Greater
Effect on Dose: kVp or mAs?
•
•
•
•
•
•
•
kVp
90
90
120
120
140
140
mAs
25
300
25
300
25
300
Brain (mGy)
1.39
17.00
3.21
37.79
5.08
65.07
Eye
1.94
20.31
3.71
49.72
5.44
69.75
Which Parameter Has a Greater
Effect on Dose: kVp or mAs?
•
•
•
•
•
•
•
kVp
90
90
120
120
140
140
mAs
25
300
25
300
25
300
Brain (mGy)
1.39
17.00
3.21
37.79
5.08
65.07
Eye
1.94
20.31
3.71
49.72
5.44
69.75
Which Parameter Has a Greater
Effect on Dose: kVp or mAs?
•
•
•
•
•
•
•
kVp
mAs
Brain (mGy) Eye
90
25
1.39
1.94
dose with inc 20.31
kVp
90RESULTS:
300 Inc 17.00
& mAs,
inc with mAs 3.71
is linear,
120
25but the 3.21
the inc300
with kVP37.79
is squared. 49.72
120
140
25
5.08
5.44
140
300
65.07
69.75
Strategies to Decrease Pt Dose
• Modulate kVp & mAs depending on pt
size & body part scanning
• Use low dose for:
– localization (dec dose: 50-65%)
– attenuation correction (dec dose:
97%)
– chest CT (lung)
– small patient
Other Strategies to Consider
• Appropriateness of the procedure
• Dec radiopharmaceutical doses (inc
imaging time)
• Dec CT acquisition parameters if a
diagnostic CT will not add to the
current available information
NM PROCEDURE DOSES
TO: the TECHNOLOGIST
US NRC Maximal Annual
Permissible Limits for Occupational
Exposure
• Whichever is more limiting:
– Total EDE OR
– Sum of deep DE to org/tissue
(except lens)
50 mSv
500 mSv
• Shallow DE to skin/extremity
• Eye/lens (nonstochastic)
• Minors (<18 yrs) 10% of above
500 mSv
150 mSv
3 Tenets of ALARA
• Time
• Distance
• Appropriate shielding
Time
• Greater time near a radiation source
→ greater exposure
• Major radiation source:
• Common clinical settings:
– dosing room, patient transfers (to
and from the imaging room/table),
imaging time, uptake time, waiting
time
Time
• Greater time near a radiation source
→ greater exposure
• Major radiation source: the patient
• Common clinical settings:
– dosing room, patient transfers (to
and from the imaging room/table),
imaging time, uptake time, waiting
time
Why are the technologists
here?
While the patient is here?
Limit their occupational dose.
Time Suggestion Strategies
• Be aware of the proximity of injected patients
• Explain proced/pt questions before inject RP
• Hall or room where injected pt are waiting to
be scanned (take an alternate route)
• Injected patient bathroom (use alternate)
• Video tracking of pt
• Work related phone or “break” near injected
patients (move the phone)
• Wait for tracer to decay
Distance
• The “Newton’s Inverse Square Law”
• The intensity of radiation is inversely
proportional to the
square of the
distance from the
source.
Intensity = 1/d2
Distance
• The intensity of radiation becomes
weaker as it spreads out from the
source since the same amount of
radiation is spread over a larger area.
• Example: Heat from
a fireplace
Shielding
• Depending on the type of ionizing
radiation, use appropriate shielding
• alpha radiation: No shielding, poor
penetration, high energy
– major concern: internal contamination
by ingestion, absorption
or inhalation
Polonium 210
Alpha Radiation Precautions
• Apply basic lab safety: NO eating,
drinking, smoking, or applying makeup in the radiopharmacy or clinic.
Shielding
• Alpha radiation precautions:
• Personal Protective Equipment (PPE)
– laboratory coat
– gloves (esp if skin is not intact)
– other
Shielding
• Beta radiation:
• Low Z shielding – plastic, glass
• No high Z due to Bremsstrahlung
radiation which is highly
penetrating
Shielding
• Gamma radiation, PET tracers:
• High Z shielding with the amount
dependent on the energy of the
radiation & HVL of the shielding
material
• Generally, 10 HVL needed to achieve
background radiation
HVL in NM
• Radioisotope
• 99mTc
• 131I
• 133 Xe
• 111 In
• 137 Cs
• 201Tl
• 125 I
keV
140
364
81
245
662
70
35.5
HVL Pb (cm)
~0.02
~0.30
~0.03
~0.10
~0.65
~0.03
~0.01
HVL in NM
• Radioisotope
• 99mTc
• 131I
• 133 Xe
• 111 In
• 137 Cs
• 201Tl
• 125 I
keV
140
364
81
245
662
70
35.5
HVL Pb (cm)
~0.02
~0.30
~0.03
~0.10
~0.65
~0.03
~0.01
Shielding
• J Nucl Med Tech (03/2011) Sonmez
et al (Turkey):
• Conclusion: 2 mm lead shield dec
NMT dose by ½ for common proced.
- TCO4 thyroid, bone, cardiac
MIBI & thallium, DMSA
- highest dose: MIBI cardiac
FDG shielded
shipping box
and syringe
shield.
Weight: 70 #
Courtesy of J Thomas
FDG syringe shield and pig
Courtesy of J Thomas
Radiopharmacy
Wheeled
cart with
FDG in
syringe
shield
enroute
to dosing
room.
Courtesy of J Thomas
Occupational Radiation
Exposure
• Primary exposures for NM
technologist:
– radiopharmaceutical preparation
– injecting patients
– radioactive patients
Occupational Radiation
Exposure
• Primary exposures for NM
technologist:
– radiopharmaceutical preparation
– injecting patients
– radioactive patients
Occupational Radiation
Exposure Issues
• Devise strategies to reduce workrelated exposure.
• What tasks expose the NMT to the
highest radiation dose?
Work-related Tasks
1. Radiopharmaceutical
preparation/administration
2. Patient transfers to & from the
imaging room; on & off the
imaging table
3. Patient imaging to include “set up”
4. Therapeutic procedures
5. PET studies
Question
• How can one minimize exposure
during those tasks with the highest
radiation dose?
• ALARA principle & monitoring
Badges: Monitor WorkRelated Dose
1. Who needs to be badged?
2. Where are the badges worn?
Badge requirements
• Anybody who is likely to receive >
10% of occupational dose limits
• Any minor or pregnant female likely to
receive >100 mrem
• Where are badges worn?
Courtesy of F Mettler
Badge requirements
• TLD or other
device usually
placed on
upper torso
Courtesy of F Mettler
• 2002 Lundberg (Australia) “Measuring
& Minimizing the Radiation Dose to
the NMT”*
• Looked at rationale for anterior torso
badging. Is it reliable to quantify
dose?
• Assumption: uniform beam, incident
from front
J Nucl Med Technol 2002;30:25-30.
• 3 dosimeters on a NMT X 3 months:
front collar, front waist, back waist
• Recorded dose q 30 min (0730-1800)
• Task recorded in journal; alternated
injecting RP & scanning; weekly
• Limitations: one NMT data
J Nucl Med Technol 2002;30:25-30.
Results
• Uniform beam confirmed: anterior
collar & waist readings similar
• Except: injection of tracers, collar
70% higher than waist (position of
NMT torso for RP injection)
• Collar readings
– more conservative
J Nucl Med Technol 2002;30:25-30.
Results
• 1/3 of the time, back > front waist
readings: likely when NMT back to pt in
imaging room or from other source
• Average doses:
• inject: 2 µSv/h/12 µSv/d/3.2 mSv/y
• scan: 0.2-2 µSv/h/5.4 µSv/d/1.4 mSv/y
J Nucl Med Technol 2002;30:25-30.
RP Preparation/Administration
• Routine handling of RP
• Activity adds to NM dose, esp fingers
• Monitor hand exposure with ring
dosimeters:
- dominant hand, base of ring
finger
Badge requirements
• Ring dosimeter
Film should be facing
usually palm
on 4thof hand
finger
(dominant hand)
Courtesy of F Mettler
Hand Exposures
• 2008 Wrzesien et al (Poland) “Hand
Exposure to Ionizing Radiation of NM
Workers”
• Measured RP finger doses with TLDs
• Reference: 4th ring finger TLD; 5 X lower
than thumb, index or middle fingers (RP
higher doses than NMT)
• 4th finger TLD may underestimate dose
Hand Exposures
• 2005 Guillet et al (France) “Technologist
Radiation Exposure in Routine Clinical
Practice with 18F-FDG PET.”
• FDG > dose but concept important
• Finger dose: 50% dec exposure with
monodose c/w multidose vials
• Data also supported: semiautomatic FDG
injector & pt video tracking
Guillet et al J Nucl Med Tschol. 2005 Sep;33(3):175-9.
Syringe Shields
Syringe Shields
• Important to significantly reduce hand
exposure in preparing & injecting RP
• Disadvantage: cumbersome
• Hand dose reduction depends on the
RP & shield material, but is generally
75 to > 90%
• Tungsten, leaded glass,
lead
Patient Transfers
• 2004 Smart et al (Australia) “Task
Specific Monitoring of NMT’s
Radiation Exposure”
• Constant monitoring of NMT q 32 sec
(0830-1700) dose rate in µSv/hr
• Pocket dosimeter at anterior waist
• Procedure journal w/ start & stop
times of individual tasks
Activities with the Highest Dose*
1. Transferring incapacitated pt from
imaging table to hospital gurney
2. Difficult injections w/o syringe shields
3. Setting pt up for cardiac gated
studies
* Smart et al Rad Protection Dosimetry Vol 109, No 3, Oxford Univ Press, 2004.
Average Doses
• Post MDP transfer: 0.54 µSv (40% of total
dose 1.3 µSv)
• Injecting 24 mCi HDP + tungsten syringe
shield: 0.57 µSv (difficult pt: 1.6 µSv)
• Setting up pt for gated MIBI:
– 1.1 µSv
– with 0.5 mm Pb apron: 0.6 µSv
– dec by factor of 2
* Smart et al Rad Protection Dosimetry Vol 109, No 3, Oxford Univ Press, 2004.
Recommended
1. While waiting for pt transfer, NMT
stands away (distance)
2. Use tungsten shield (shielding)
3. Use of a 0.5 mm Pb apron for high
activities of Tc99m (shielding)
* Smart et al Rad Protection Dosimetry Vol 109, No 3, Oxford Univ Press, 2004.
Question # 4
• Which NM technologist task is
generally associated with the highest
work-related dose?
•
•
•
•
A. Radiopharmaceutical preparation
B. Radiopharmaceutical injection
C. Patient scanning
D. Patient transfers
Question # 4
• Which NM technologist task is
generally associated with the highest
work-related dose?
•
•
•
•
A. Radiopharmaceutical preparation
B. Radiopharmaceutical injection
C. Patient scanning
D. Patient transfers
In the final
stretch….
….so stand
up & stretch!
Patient Imaging
• Injected pt is a significant radiation source
• NM imaging times are extended
• Rec: depending on pt condition & imaging
protocol, NMT need not remain in room
• Time & Distance tenets (ALARA)
• Average 0.3-3 mrem/procedure to NMT of
which 50-90% can come from imaging*
* Mettler
Scanning Doses: Many
Variables
• RP
• Administered activity
• Amount of pt contact, dec with pt
requiring no or limited assistance
• Back doses: 30% of front doses
• Procedure type
Variability with Procedure Type
• Highest:
• MUGA > stress MIBI & Bone scans
• Lowest:
• Thyroid, thallium cardiac
• Post I31I WBS low with “distance”
Higher Dose Procedures
• MUGA/cardiac:
– high administered activities
– pt contact during “set up” time
• Bone scans:
– potentially high dose with inc pt contact
– limited contact once pt is on the
imaging table
Question # 5
• Which NM procedure is generally
associated with the highest NM
technologist occupational dose?
•
•
•
•
A. Bone SPECT
B. MUGA
C. 131I post therapy scan
D. Stress Tc99m MIBI
Question # 5
• Which NM procedure is generally
associated with the highest NM
technologist occupational dose?
• A. Bone SPECT
• B. MUGA
FDG vs General NM Exposure
•
•
•
•
2 yr prospective study
PET/NM (quarterly): 771 & 524 µSv
Estimated PET proced dose: 4.1 µSv
FDG IV (w/o & w/ 1° shield): 2.5→1.4
µSv
• Trolley-mounted 2° shield: 3.6→1.9
µSv
*Roberts FO et al “Radiation Dose to PET Technologists & Strategies
to Lower Occupational Exposure.” J Nucl Med Technol.2005 Mar;33(1):44-7
PET NMT Task & Scheduling*
• PET/CT: 8-10 studies/day
• 2 technologists: weekly rotation of
FDG injection and scanning to include
pt transfers
• Q 3 month rotation (preferably per yr)
* Teaching site in San Antonio, Texas
PET NMT Tasks
• Injection:
– Time: < 30 sec (IV running before)
explain procedure to pt before
inject FDG & answer questions
– Distance: close to pt & FDG
– Shielding: PET syringe shield in a
shielded carrier in shielded room
PET NMT Tasks
• Scanning/Pt transfer:
– Time: 1-2 min (pt w/o assistance);
scanner is in adjacent room; brief
re-explanation, pt on & off table,
position pt
– Distance: close
– Shielding: Pb glass in scanner
control room
2009
NMT Ring (mrem) Body
1st
A
B
A
B
A
B
A
B
2nd
3rd
4th
136
669
425
483
629
92
254
2407
110
126
141
111
250
78
115
262
NMT PET exposures
•
•
•
•
2009 (quarterly rotation of 2 NMT)
Ring dose >> body dose (factor 2-4)
Ring: 636/483 mrem (2 outliers)
Body: 149/142 mrem
• 2010 (2 quarters)
• Ring dose twice body dose
• Ring 151 mrem; Body 78 mrem
NMT PET exposures
•
•
•
•
2009 (quarterly rotation of 2 NMT)
Ring dose >> body dose (factor 2-4)
Ring: 636/483 mrem (2 outliers)
Body: 149/142 mrem
• 2010 (2 quarters); NMT education!
• Ring dose twice body dose
• Ring 151 mrem; Body 78 mrem
Summary
• Inc medical imaging using ionizing
radiation, CT, NM, VIR (1980)
• Concern for latent effects of radiation
(CA induction, genetic effects):
medical, epidemiological, economic
Summary
• Inc NM procedures, inc occupational
exposure (NMT)
• NRC limits & ALARA, can help
reduce & minimize work-related
exposure
• Strict adherence: time, distance,
shielding
• Monitoring: wear badges